Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $106.41   6.823%   $113.6704   $113.67   $113.65   $113.70  
  Purchase #2 $156.29   8.229%   $169.1511   $169.15   $169.15   $169.20  
  Purchase #3 $222.99   9.700%   $244.62   $244.62   $244.60   $244.60  
  Purchase #4 $75.82   11.763%   $84.7387   $84.74   $84.75   $84.70  
  Purchase #5 $231.83   7.478%   $249.1662   $249.17   $249.15   $249.20  
  Purchase #6 $222.68   11.564%   $248.4307   $248.43   $248.45   $248.40  
  Purchase #7 $144.28   12.386%   $162.1505   $162.15   $162.15   $162.20  
  7 purchase totals = $1,160.30       $1,271.9276   $1,271.93   $1,271.90   $1,272.00